Removal of arsenic from lead bullion



I Patented May 5, 1931 UNITED STATES v RONALD CAIPBELL B'O'THERFORD, OF PASO, TEXAS, ASSIGNOR AMERICAN REFINING COMPANY OF NEW YORK, N. Y., A CORPORATION OF NEW SMELTING AND JERSEY I Rolirawlng. Application fled July 26,

This invention relates to the smelting of lead, and more particularly to a new and improved method of reducing the arsenic content of lead bullion during the smelting oper- 1ation to a suflicientl low value to facilitate the subsequent re ning operations.

The invention provides for substantially eliminating arsenic in lead bullion by the proper control of the reduction and the constituents of the bullion and without introduction of reagents other than those originally present. p

. The invention further provides for thereduction of the arsenic content without requiring a sufliciently strong reduction to mechanically injure the apparatus or mate rially lessen the life thereof.

The invention further consists in the new and novel features of operation and the new go and original arrangements and combinations of steps in the process hereinafter described and more particularly set forth in the claims.

Although the novel features which are believed to be characteristic of this invention will be particularly pointed out in the claims appended hereto, the invention itself,- as toits objects and advantages, the mode of its operation and the manner of its organization may be better understood by referring to the 30 following description in which a particular commercial embodiment thereof is disclosed. It will be understood, however, that the processes and. the steps thereof may be modified in various respects without departing from the broad spirit and scope of the invention. In the following description and in the claims the various steps in the process and the details comprising the invention will be identified by specific names for convenience, but they are intended to be as generic in their application as the art will permit.

The invention in general'colnprises the reduction and removal of arsenic as speiss. For this purpose it has been found that a sufiicient amount of speiss forming material, such as copper, must be present in the charge to combine, with the arsenic and prevent the same from becoming alloyed with the lead, in which case it could not be readily removed with the dross. If the charge also contains PATENT OFFICE nmovu. or ARSENIC mom LEAD Bur-1.101s

1929. Serial No. 881,397.

sulphur the copper will first combine with the sulphur to produce a matte, or if there is no avaliable sulphur present, the copper is either all carried out with the lead or subscquently drossed off, or it unites with the arsenic and iron to form speiss.

In accordance with the present invention the conditions are so controlled that a sufficient amount of copper is present in the I charge after the sulphur has been removed to unite with the arsenic and iron to form speiss,

which contains substantially the entire arse-.

is necessary to reduce the sulphur content to I a minimum unless a large amount of copper is available. This may be effected in any convenient manner such as blast roasting or sintering.

After the ore has been thus treated and the sulphur reduced to the desired limits it is placed in the blast furnace and smelted in the usual manner. During the smelting operation any sulphur that is available for matte making, will combine with a portion I of the copper present and form matte. Some of the remaining copper will then, provided the reduction is good, combine with metallic iron and arsenic to form a speiss. The balance of the copper asses off with the lead bullion and is su scquently removed in the drossing kettles.

" The greater'part of the speiss formed in the blast furnace can be collected in the forehearth or settler and removed from time to time in the same manner as matte. The balance of the speiss will go with the lead and subsequently be collected in the dross. The bullion produced from this operation. willbe substantially free from arsenic.

It has been found that the arsenic content can be reduced to .0572 or less, provided .8% to 1% of copper is present in the charge. In fact, the arsenic'content has been reduced to 02% when the process is carried on with the proper amount of reduction. The range through which copper and arsenic unite to the charge going into these furnaces contained ap roximately 1.0% copper and 0.7% arsenic. Rs a further instance, a charge con taining 0.8% copper and 0.2% arsenic has produced a bullion averaging 0.03% arsenic. As a still further example, a charge containing 4.0% copper and 0.4% arsenic was smelted by the above process and produced a bullion in which the arsenic did not w exceed 0.03%.

As a specific example of the manner in which this process is carried on, an ore containing 29.5% lead, 6.3% copper, 28.2% sulphur, 0.7% arsenic and 5.1% zinc, was roasted on the sintering machine whereby the sulphur was reduced to 2.0%. The sinter, along with the necessary fluxes, coke and direct smelting or oxidized ores, was charged into a blast furnace and smelted in the usual manner. On smelting there resulted slag, matte, speiss and bullion. The slag contained small amounts of copper, lead and sulphur and a trace of arsenic. All the remaining sulphur was combined with the copper in a matte which was of substantially the follow analysis: copper 30%, lead 10%, iron 30%, sulphur 20%.

Due to the low sulphur content of the blast furnace charge there is not sufficient sulphur present to combine with all the copper or matte. Part of the remaining copper accordingly combined with the arsenic and iron to form speiss, the composition of which was approximately as follows: copper 40%, iron 30%, lead 10%, arsenic 15%. It is obv ous that the speiss produced may vary acslderably from the above, although in all probability it would be relatively high in copper and low in arsenic, due to the fact that the ore contained a higher percentage of copper and low arsenic. All of the remaining copper in the charge was carried 05 with the lead and subsequently drossed o In the above charge approximately onehalf of the copper is available for matte making and if a matte with 30% copper and 20% sulphur was produced this would only contain one-four of the total copper. About onehalf of the remaining copper would go in with the speiss and the balance into the bullion and slag.

It may be noted that in 100 tons of the above mentioned ore, the charge would contain 6.3 tons of copper and0.7 tons of arsenic. The matte formed would contain 1.5 tons of copper while the speiss would account for practically all the arsenic and about .2 tons of copper. The remaining 2.8 tons of copper would pass out with the bullion, less a small amount inthe slag.

With a charge of this character no dilficulty is experienced in producing bullion very low in arsenic, provided fair reduction is maintained, because the sulphur on the charge is low and the copper is sufliciently high to take care of all available sulphur and also the arsenic.

As a further specific example, We may consider an ore of the following analysis: lead 22.8%, copper 1.1%, sulphur 15.5%, arsenic 1.8%, zinc 13.9%.

The above ore may be first roasted on a sinterihg machine to reduce the sulphur content to 2.0% and then smelted in the usual manner with the addition of the necessary fluxes. This charge would produce practically no matte, due to. the low copper and sulphur content and the high zinc content.

A 100 ton charge of this ore would produce 1.1 tons of copper, 2 tons sulphur and 1.8 tons of arsenic. All of the sulphur and about 0.2 tons of copper would go into the slag.

With strong reduction the remaining copper might, along with iron, combine With all the arsenic and form speiss and such a speiss would probably contain copper 10%, iron 50%, arsenic 30% and lead 5%. Strong reduction is hard to maintain continuously, so with this type of charge it might be advisable to increase the copper content by the addition of some copper bearing ores or by-products. A charge containing still more arsenic and less copper than the above example would certainly require the addition of copper in orderto make the operation successful.

The success of the operation is dependent on three things, namely, low sulphur, sufficient copper to combine with the arsenic to form speiss and good reduction. The higher the copper on charge, assuming the arsenic percent-age in the charge is a fixed quantity. the less care is necessary With respect to the strength of reduction and the amount of sulphur in the charge.

In the above described example copper has been assumed to be present in the ore. It is obvious that the copper may be in the form of copper bearing ore, concentrates, smelter byproducts and other forms, the essential feature being in having the copper present in sufficient quantities to unite with the arsenic and produce speiss.

Although certain novel features of the invention have been shown and described and are pointed out in the annexed claims, it will be understood that various omissions, substitutions and changes in the several steps of the process and in its operation may be made 1,eos,771-

by those skilled in the art without departing from the spirit of the invention.

vWhat is claimed is: I y

1. The process of smelting a lead ore con"- taining 20% to 30% sulphur, 0.5% to'1% arsenic and 1 to copper, which comprises roasting said ore to reduce the sulphur content ,to approximately 2% and smelting said ore whereby the copper combines with the remaining sulphur to produce matte and 10 with the arsenic to produce speiss, whereby the arsenic content of the base lead'bullion is reduced to less than .03%.

v 2. The process of treating lead ore containing sulphur,-copper and arsenic to produce artia-lly refined lead, which comprises roasting said, ore to reduce the sulphur con- .tent to less than the chemical equivalent of the copper content whereby an excess of copper is available to unite with the arsenic, and smelting the roasted ore to cause the copper to unite with the remainder of the sulphur and form matte and the excess of copper to unite with the arsenic to form speiss, and .removing the matte and speiss from the residue which comprises a base lead bullion containing less than .05% of arsenic.

3. The process of treating lead ore contain-' ing sulphur, copper and arsenic to produce a ..base lead bullion containing low arsenic,

which comprises roasting said ore to reduce the sulphur content to a point such that the copper is present in a quantity chemically. uivalent tothe combinedquantity of sulp ur and arsenic, then smelting the material to cause the copper to unite with the sul hur and form a matte and with the arsenic orm speiss, whereby the arsenic content of the base lead bullion is reduced to less than 05%. 40 4. The process of treating lead ore containing sulphur, copper and arsenic to produce a base lead bullion containing low arsenic, which comprises roasting sald ore toreduce the sulphur content to a point such 40 that the copper is present in a quantity chemwally equivalent to'the combined quantity of sulp ur and; arsenic in a sufliciently strong reducing-atmosphere to assist in the formation of speiss, then smelting the material to.

: cause the copper to unite with the sul hur 5my hand.

" and form a matte and with the arsenic orm speiss, whereby the arsenic content of the base lead bullion is reduced to less than .05 In testimony whereof I have hereunto setnorm. mm scream-0RD. 

